Targeting protein translation for cancer therapy is an attractive strategy to limit cancer cells proliferation by depriving them of essential nutriments. However, the currently available drugs target components of the protein translational machinery that are also essential for normal cell functions. Here, we propose to develop a more rational approach by targeting a regulator of protein translation in cancer cells. Our preliminary data indicate that the stress-activated RNA binding protein hnRNP A18 confers growth advantage to cancer cells by regulating the expression of key proteins that prevent apoptosis and/or increase DNA repair. hnRNP A18 increases protein translation by binding to a specific RNA signature motif in the 3'UTRs of its targeted transcripts and interacting with the general translational machinery. Therefore, targeting hnRNP A18 could prevent protein translation in cancer cells, where hnRNP A18 is over expressed, and would only affect the translation of transcripts harboring hnRNP A18 signature motif. Our working hypothesis is that rational targeting of hnRNP A18 will inhibit the translation of specific RNA transcripts devoted to confer growth advantages to cancer cells. To test this hypothesis three specific Aims have been designed. Aim 1: Determine the role of hnRNP A18 in cancer cells sensitivity to anticancer treatments. Levels of hnRNP A18 will be manipulated and the cellular sensitivity to clinically relevant doses of anticancer drugs or radiation will be analyzed by clonogenic survival assays, apoptosis and DNA repair (?H2AX). Aim 2: Characterize the biochemical and functional binding activity of hnRNP A18 to its targeted transcripts and evaluate the effect of hnRNP A18 on cancer progression. This will be performed by systematically analyzing binding to the different stems and bulges of the hnRNP A18 RNA motif and evaluating the effect of hnRNP A18 phosphorylation on the binding to these different RNA structures. Aim 3: Determine the three-dimensional structure of hnRNP A18 and identify the hnRNP A18-RNA binding interface. The structures of unphosphorylated and phosphorylated hnRNP A18 in the absence (apo) and presence of 3'UTR RNA (signature motif) will be solved in solution by Nuclear Magnetic Resonance (NMR) spectroscopy. Our long term goal is to develop drugs that could target hnRNP A18 to control and possibly stop cancer progression. This could be accomplished by solving hnRNP A18 three dimensional structure and use computer-aided drug design (CADD) technology to identify small molecules that could target hnRNP A18.